BMFA Indoor Technical Committee

THE Site for UK Indoor Duration Flyers

Indoor Model Classes

The modelling spans over 100 years, take a look at this article to see how far it has come over the years.

Here’s an overview of the main classes that are flown in the UK, together with a guide as to what is involved in their construction and flying etc. There's an indication of the skill required for each aspect of construction and flying: L – Low – no previous experience needed, M – Medium – some previous modelling experience needed, H - High – previous indoor modelling experience is necessary.

For full rules covering the International classes F1D, F1M, F1L, F1R, F1N please refer to the FAI website here.

Gyminnie Cricket (GC), Entry level model, unlimited rubber

Wood: L, Build: L, Covering: L, Rubber: L, Flying: L

The GC is available as a kit from the BMFA which makes a c9 gram model with a plastic propeller. Making your own propeller from balsa wood can reduce this to around 3 gm. - a model with a reasonable duration performance. Most National competitions are for models conforming to this weight and they must use the same flying surface outlines motor stick/boom lengths as the original. A balsa sheet propeller is allowed. It will take about 5 hours to build.

The idea of this model is to provide a follow on from the GC to a recognised Class (F1R) but with an easy build, there are no rolled tubes, a balsa sheet prop. and no curved outlines to deal with. The model has a performance similar to an F1L, at the minimum weight of 1 gram which can be achieved without too much difficulty. It complies with the competition rules for 35 cm but at this weight will obviously not compete with ultra light models. You can expect to achieve 10 minute flights in a 20’ Sports Hall. It will take you about 10 hours to build.

A fun little model, with a great performance. Small wood sizes a bit tricky and flying on high torque can resemble a 3D aerobatic performance! Quick build, about 5 hours, some previous experience ideally.

This is a long established class. Basically 18” projected wingspan with a maximum chord of 3”, this makes the wing rather long and thin and as a result needs care to make a stiff airframe. It is more of a challenge to achieve the 1.2 gm minimum weight than the 35cm Entry level model. Still quite quick to build at around 10 hours.

35cm (F1R) International Class, apart from minimum wingspan of up to 35cm there are no rules!

Wood:H, Build:H, Covering:M, Rubber: H, Flying: H

Bob Bailey has described this class as perhaps the most challenging as there is no minimum weight rule, currently sub 400 mg models hold the records! They are lovely models, even when built a little heavier they perform wonderfully well. They can match an F1D model’s duration. People like them because they hold their trim well due to having rolled balsa tubes for motor stick and tail boom. Not an easy build though due to small wood and rubber sizes and need for VP in competition.

Much bigger wood sizes make it an easier build, but VP propeller necessary for competition takes it to a new level. Personally I find it a big model that has much the same level of difficulty as an F1D but not as pretty to fly.

This is the class that is flown in the Indoor World Championships. Lovely models to build and fly but you do need some indoor building experience before giving one a try! Also a Variable Pitch propeller is a must, though the hubs are now available commercially – at around 80EUR from Ivan Treger - see under Suppliers section.